Battborg/PicoBorg Reverse/Adafruit Servo Hat

Submitted by richard.jackson... on Thu, 02/12/2015 - 17:53

Forums:

I am converting an RC truck into a cambot using a picoborg reverse for the drive and steering and adafruit servo hat for camera pan and tilt and other sensors.
I have a 9.6v Mi-mh battery pack which I believe I can use to power the set up however, before I connect anything I want to check the connections to the Rpi 2B.
If I use a Battborg to supply the 5v for the pi, I think, I need a parallel connection from the battery pack to the motor power input connections between the motor outlets. The Adafruit hat ( http://www.adafruit.com/products/2327 ) appears to have the same requirement to power the servos but delivers power to the Rpi via the GPIO. I have attached a diagram which may be clearer.
In essence I am worried that the supply from both Adafruit Hat and Battborg may damage the Rpi what do you think ?.

Attachments: 
Cambot Power.pdf
piborg's picture

piborg

Fri, 02/13/2015 - 11:01

Ideally you do not want both the BattBorg and the Adafruit Servo Hat to provide 5v to the Raspberry Pi at the same time.

The Adafruit Servo Hat comes with a connector which covers all 40 pins of the GPIO connector, blocking the 6 pins the PicoBorg Reverse wants to be connected on to.
So I guess the way you would separate the 5v so that the Raspberry Pi is only supplied from one of the boards depends on how you intend to share those 6 GPIO pins between both boards.

How are you intending attach both boards to the Raspberry Pi so that they share the GPIO?

richard.jackson...

Fri, 02/13/2015 - 11:29

I hadn't twigged that the Adafruit board supplied power to the Rpi until I started to dig into the detail I thought it was similar to the reverse but for servos. The Adafruit board is delivered without the 40pin connector soldered up so that a stacking connector can be attached in effect once installed there will be a row ow pins available to pin another connector or individual wires to. An option I guess might be to rely upon the battborg for the reverse board power but only connect the two control pins to the 40 pin header leaving the Adafruit to power the Rpi maybe taking the 5v and ground to supply the Adafruit board.
Wgat do you think ?

piborg's picture

piborg

Fri, 02/13/2015 - 12:14

The control chip on the PicoBorg Reverse uses the 3.3v pin to get power, but should only use a small amount.

I would suggest you try running without the BattBorg first, attaching the PicoBorg Reverse normally on top of the extended GPIO pins from the Adafruit Servo Hat.
It is likely that there will be enough power provided to cover all of the boards that way.

If doing that does not provide enough power for everything to run then it might be better to connect the Adafruit Servo Hat in a way which does not connect up to the 5v pins, then connect the BattBorg to the PicoBorg Reverse and use it to power the Raspberry Pi instead.

richard.jackson...

Fri, 02/13/2015 - 12:26

OK Thanks for that. I have to get the extended header and solder it all up before I can try it. In the mean time I have got the battborg and reverse running the Rpi and powering the motors via the gui using a vnc terminal.

I'll let you know how I get on with the servo hat when I've got it wired up etc.

richard.jackson...

Tue, 02/24/2015 - 11:21

Success!! It turns out the Adafruit board does not back feed 5v to the Rpi therefore the solution was to buy an extra battborg to supply 5v to the Adafruit board leaving the Picoborg Reverse/Battborg combination to supply the Rpi.
Now just a case of preventing the servos moving on boot up from their required ranges - one servo horn broken so far.......

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